Tension testing of building units

ABSTRACT

Building units, such as concrete blocks, are tested by inserting an expandable member within a core of the block with means for applying uniaxial force from the expandable member against opposite walls of the core at the appropriate location and properly oriented so that the force is distributed along such walls, and increasing the force until the walls fracture, the force required to fracture the wall being measured by the apparatus.

United States Patent 1 Holm et al.

[111 3,792,608 [4 1 Feb. 19, 1974 TENSION TESTING OF BUILDING UNITS [75] Inventors: Thomas Holm, Waldwick, N.J.;

Lester K. Childress, Richmond, Va.

[73] Assignee: Solite Corporation, Richmond, Va.

[22] Filed: Sept. 8, 1972 [21] Appl. No.: 287,313

Related US. Application Data [63] Continuation-impart of Ser. No. 75,907, Sept. 28,

1970, [52] 11.3. C1. 73/97, 73/14] R [51] Int. Cl. G01n 3/10 [58] Field of Search 73/88 R, 88 E, 95, 97, 93, 73/103, 141 R, 87; 177/146, 208; 254/93 R [56] References Cited UNITED STATES PATENTS 1,343,611 6/1920 Berger 73/87 2,686,047 8/1954 Duncan 254/93 R 3,111,840 11/1963 Barnet et al. 73/97 X 3,122,916 3/1964 Sedlacek 73/97 3,446,062 5/1969 Goodman et a1 73/88 E 3,693,424 9/1972 Wagle 73/120 FOREIGN PATENTS OR APPLICATIONS 967,813 8/1964 Great Britain 73/141 R OTHER PUBLICATIONS Malhotra et al., Ring Test for Tensile Strength of Concrete, Materials Research and Standards, pp. 2-12, Jan. 1966.

Primary Examiner-Charles A. Ruehl Attorney, Agent, or FirmA. Yates Dowell. Jr.

571 ABSTRACT Building units, such as concrete blocks, are tested by inserting an expandable member within a core of the block with means for applying uniaxial force from the expandable member against opposite walls of the core at the appropriate location and properly oriented so that the force is distributed along such walls, and increasing the force until the walls fracture, the force required to fracture the wall being measured by the apparatus.

9 Claims, 11 Drawing Figures PATENTED FEB] 9 I974 SHEET 3 OF 3 TENSION TESTING OF BUILDING UNITS CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of application Ser. No. 75,907 filed Sept. 28, 1970 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to construction material and more particularly to building units or blocks having a core opening. These blocks are used for the construction of masonry walls which are subjected to stress in various directions. However, due to changes of condition from various causes including shrinkage, thermal change and settling of the ground, tensile forces are induced. Where failure occurs in a masonry wall, this is generally due to such tensile forces.

2. Description of the Prior Art Hertofore building blocks have commonly been tested in a compression test even though the strength of brittle materials is determined by the ultimate tensile strength, on the theory of correlation between compression and tensile strength of the block. However, the correlation has varied so that the results of the compression test have not been satisfactory for establishing the tensile strength of the block. Substantially all nonstructural failures, such as cracks due to moisture change, carbonation, temperature stresses, or restrained frame movements and the like, result in excessive tensile stresses which are not evident in compression tests.

Apparatus for tension testing of block has been used in a limited manner. Such testing is described in the paper entitled Tensile Testing of Concrete Block and Wall Elements by Richard O. Hedstrom, published in the Journal of the Portland Cement Association Research and Development Laboratories, May. 1966. The paper describes the test as including the use of highstrength resin bonding agents for attaching the ends of the block to heavy steel plates which are mounted in a hydraulic rarn of the type used for tension testing of steel, in which the force is applied externally.

The foregoing procedure is substantially restricted to the laboratory since it requires bonding of the block to strong plates and the use of heavy, stationary equipment which may be transported and set up only with difficulty. Also, the bonding process normally requires at least 24 hours to achieve the required strength and thereafter substantial care must be exercised to preclude the introduction of eccentric forces in the stationary equipment which would impart a false indication of the tensile strength of the block. This technique substantially has been discarded due to its cumbersome nature as well as the expense and the difi'rculty of eliminating eccentric loading.

SUMMARY OF THE INVENTION Briefly stated, the invention includes a small lightweight portable ram which is of a size to be received within the core of a building block and apparatus associated therewith by means of which force is applied by the ram against opposite walls of the core in a uniaxial direction in order to obtain an accurate reading of the tensile strength of the walls. The invention includes the provision of apparatus for positioning the ram in the core and for applying its force in the proper direction butions, the invention also includes the provision of ad- 1 justable plate members by means of which a single ram may be used to test various blocks, thereby reducing the amount of equipment which may be required for testing such blocks.

It is an object of the present invention to provide an apparatus and method for the tension testing of building units such as blocks which permits the block to be easily and rapidly tested on the job with a minimum of lightweight, inexpensive equipment which can be easily transported and used by persons having ordinary skill.

Another object of the invention is to provide an hydraulic ram which is inserted into the core of a concrete masonry unit and which develops a piston force that is transmitted through a load distribution system in a manner that the masonry unit becomes a monolithic frame under load.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective illustrating one application of the invention.

FIG. 2 is a top plan view of the shoe members located in the core of a building block.

FIG. 3 is a section illustrating the shoe member in expanded position to fracture the block.

FIG. 4 is a section on the line 4-4 of FIG. 2.

FIG. 5 is a section on the line 5-5 of FIG. 2 and illustrating the inner shoe member.

FIG. 6 is a front elevation of the outer shoe member.

FIG. 7 is a rear elevation thereof.

FIG. 8 is a perspective of a selectively usable shim.

FIG. 9 is a top plan view of a building block having unequal wall thicknesses and indicating the elastic curve of the monolithic block when uniaxial force is applied.

FIG. 10 is a fragmentary top plan view illustrating the initial fracture of the block of FIG. 9.

FIG. 11 is a fragmentary section illustrating the complete fracture of the block.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With further reference to the drawings, conventional masonry building units B and B are disclosed having a pair of core openings C and C, respectively. The unit B (FIGS. 1-5) has side walls W1 and end walls W2 of substantially uniform thickness in a horizontal plane while the unit B(FIGS. 9-11) has side walls W1 of greater thickness than the end walls W2 in a horizontal plane. Each of the walls W1, W2, W1 and W2 may have a constant thickness in a vertical plane or may have tapered enlarged portions adjacent the bottom of the unit, as illustrated in FIGS. 4 and 5. The object of the test is to evaluate the tensile strength of the side walls W1 and W1. In carrying out the invention, this is accomplished by distributing a force in a uniaxial direction which is parallel to the walls W1 and W1 and applying such force against the transverse end walls W2 and W2 until fracture of at least the side walls W1 and W1 occurs.

The apparatus for applying such force includes a ram 10 having a head 11 from which a piston 12 extends. The ram head is connected by a flexible hose 13 to a pump 14 having an operating handle 15 by means of which fluid pressure may be applied for extending the piston 12. Mounted in the line between the pump 14 and the ram is a gauge 16 for registering the force or pressure being applied. The gauge preferably has a first hand 17 which is directly responsive to the pressure being applied and has a second hand 18 which registers the maximum force or pressure applied until released by conventional means.

In order that the ram may be located in a desired position and its force properly directed, the invention includes a pair of shoe members 20 and 21. The shoe member 20 includes a pair of plates 22 and 23. Plate 22 has an end wall 25, a side wall 26, an inner wall 27 and a top wall 28. The walls 25, 26 and 28 are preferably formed integrally and joined by smooth, curved comers. The lower portion of the walls and 26 may taper slightly inwardly in order to facilitate insertion of the plate within the core. Plate 23 is formed generally similarly to plate 22 but of reverse configuration in order to be located adjacent to opposite walls of the core. Thus plate 23 includes end wall 5, side wall 36, inner wall 37 and top wall 38.

In order to transmit the force from the ram to the end walls 25 and of the plates, a block 40 is provided which is of such size as to be easily received within the confines of the opposed plates 22, 23. The block has an inner wall 41 and an outer wall which includes spaced pads 42, 43 between which there is a recess or depressed portion 44 of the block 40. The pads 42 and 43 extend the height of the block and are of sufficient width to engage a substantial area of the walls 25 and 35 of the plates. The pad 42 is welded or otherwise connected to the wall 25 of plate 22, while pad 43 is free to adjust along the wall 35.

For convenience in handling the plates, as well as to connect the plates 22 and 23 together in adjustable assembled relationship, each plate has a stud 46 extending upwardly from the upper walls 28 and 38. A strap 47, having an opening 48 and an elongated slot 49 for receiving the studs, is provided for holding the plates in adjustable relationship in order to provide a unitary shoe member.

Block 40 has a ledge member 50 extending laterally from its lower end and from its inner side 41. Member 50 has a threaded opening 51 to receive an adjusting bolt 52'having a turning eye 53 beneath the ledge member, whereby the end 54 of the bolt provides a vertically adjustable support for the ram 10.

Shoe member 21 is generally similar to shoe member 20 except that the inner walls of the plates and the adjustable bolt are omitted. Thus, shoe member 21 includes plates 22' and 23. Plate 22' has end wall 25', side wall 26' and top wall 28'. Plate 23' has end wall 35', side wall 36' and top wall 38. Extending upwardly from the top walls are studs 46 which are connected by a strap 47' having an opening 48 and an elongated slot 49. Block 40 has pad 42 connected to the end wall 25 and spaced from pad 43' by recess 44.

Since the dimensions of the cores vary, it may be desirable to have an additional thickness of plate for transmitting the force of the ram. Such additional plate or shim is indicated at and includes a main plate member 61 which is substantially flat having a ledge 62 extending laterally from one of its faces adjacent its upper end and adapted to overlie one of the blocks 40 and 40 to support the shim.

In order to insure that the force from the ram is transmitted in a direction which is parallel with the axis, the

. piston is preferably provided with a ball insert 12' in its outer end which engages the adjacent block or plate.

As illustrated in FIGS. 5 and 7, the lower extremities of the side walls 26, 26' and 36, 36' are provided with a slight taper to facilitate insertion into the core opening. It is contemplated that the lower extremities of such sides could be curved or tapered over a greater portion to accommodate certain building blocks having a wall structure which is thicker at the bottom than at the top. It will be understood that the configuration of the side walls 26, 26 and 36, 36; will be complementary to the wall structure of the block and spaced slightly therefrom when in use so that the outward force will be distributed over a major portion of the walls of the block which are engaged by the shoes 20 and 21. In this manner, the engaged walls apply tensile forces to the non-engaged walls and eccentric forces on such non-engaged walls are substantially avoided.

In the operation of the device, the block B or B is placed on any surface which is preferably horizontal. The shoe members 20 and 21 are placed in one of the core openings C or C in such a manner that the end walls 25 and 35 of shoe member 20 engage the inner surface of one of the walls W2 or W2 and the end walls 25 and 35 of the shoe 21 engage the inner surface of an opposed wall W2 or W2, with the concave portions of the shoe members facing each other. The side walls 26 and 36 of shoe member 20, as well as the side walls 26 and 36' of shoe member 21, are adjusted outwardly until such side walls are located adjacent to but spaced from the walls W1 or WI. The bolt 52 is adjusted so that when the ram 10 is lowered into the space between the shoe members with its lower extremity resting on the end of the bolt 54, the axis of the piston 12 is substantially coincident with the center of gravity of the side walls W1 or W1 of the core opening.

If the walls are of substantially constant thickness throughout the height of the building unit, then the axis of the piston is located generally midway of the height. However, in some blocks the walls vary in thickness from bottom to top and in cases where they are thicker at the bottom, the height of the bolt will be correspondingly lowered in order to lower the axis of the piston. The desired position of the piston may be determined ahead of time and a table prepared for use by the technician. In addition, the technician is able to determine from the nature of the fracture whether the positioning of the piston is correct. Thus, one or two trial and error fractures may be made for a particular type of block, if desired.

The recesses 44, 44 in the metal blocks which are connected to the plates insure that the application of the force is directed over a substantial area of the face of the block instead of being concentrated at or near its center which might occur if the block 40 were substantially flat along its outer face. Thus, the spaced pads 42, 43, and 42', 43 provide for distribution of the force over a major portion of the inner faces of opposed core walls. The plates of the individual shoe members have end walls 25, 35 and 25, 35' which are flat in order to engage the transverse surfaces of the end walls of the core and the application of force through the pads of the blocks 40 and 40 is spaced substantially inwardly from the sides of the end walls in order to avoid the application of force immediately adjacent to the comers of the core which might result in the forces being applied in the direction other than parallel to the side walls W1 or W1 of the block.

In the event that the length of the core openings is greater than normal, the shim plate 60 is mounted on the block 40' for engaging the piston 12 and transmitting the force to such block.

After the ram unit is positioned between the blocks 40 and 40', the pump 14 is operated to extend the piston 12 and apply a uniaxial force to the walls W2 and W2, as shown by force lines F in FIG. 9. The distributed uniaxial force causes bending moments throughout the entire building unit, including the unloaded core area, due to the unit acting as a continuous, monolithic and elastic masonry frame. The applied bending moments form an elastic curve of deformation illustrated by phantom lines E in FIG. 9.

The operator continues to operate the pump 14 to apply a distributing force to the walls W2 and W2 which causes such walls to bend slightly within the elastic limits of the building unit, while applying tension forces to the side walls W1 and W1, as illustrated in FIGS. 2 and 10. When the masonry unit includes walls W1 and W2 of equal thickness (FIGS. 1-5), force on the end walls W2 is increased until the tension forces on the side walls W1 cause such side walls to fracture, as illustrated in FIG. 3. When the side walls W1 are substantially thicker than the end walls W2 (FIGS. 9-11), the applied force on the opposed walls W2 causes a tensile stress to be applied to the side walls W1; however, since the end walls are weaker than the side walls, the tendency is for an initial fracture to occur in the end wall W2 (FIG. 10). When the end wall fractures, a bending moment is instantly applied to the side walls W1 which causes such side walls to fracture immediately after the end wall fractures (FIG. 1 1).

As soon as the building unit fractures, force within the ram is relieved since the piston 12 no longer meets any substantial resistance. The operator or technician then observes the position of the hand 18 on the gauge 16 to determine the tensile strength which was required to fracture the building unit.

Several methods of frame analysis are commonly used by structural engineers in the determination of forces, including slope deflection, moment distribution, and variations of these two basic techniques. Due to the symmetrical nature of a masonry unit about a longitudinal center line, such unit lends itself to a variation of the moment distribution technique in which the joint distribution factors are adjusted to account for symmetry, with carry-over moments distributed in one direction only. Each configuration of masonry unit requires a separate analysis due to different relationships between thicknesses of the side walls W1 and W1 and the walls W2 and W2, however, such analysis is easily completed, since there are a limited number of mold formats available. Once the moments are determined, the bending stress distributions are algebraically added, where applicable, to the axial stresses and final stresses are determined.

Reasonable agreement, with theoretical calculations, has been developed in an investigation in which strain gauges were applied at various locations to a masonry unit and readings of the strain gauges were taken at spaced intervals.

Additionally, the operator can judge whether the ram has been properly positioned by the nature of the fracture. With reference to FIGS. 1-9, when the ram is properly positioned, the fracture occurs along both side walls W1 substantially simultaneously and in a line that is substantially vertical. With reference to FIGS. 9-11, when the ram is properly positioned, the initial fracture occurs substantially midway of the wall W2 and immediately thereafter both of the side walls W1 fracture substantially simultaneously along a generally vertical line. The wall portions which break away from the building unit B or B as a result of the fracture, move only slightly initially until they topple over. If, however, the inner movement of the separated end portions is substantially other than translational as, for example, by one side moving outwardly more rapidly than the other, then the operator should recognize the need for appropriate adjustment in order to more nearly apply the force in the proper direction. For example, if the upper end of the separated portion moves away more rapidly than the lower end, the operator would realize that the ram was applying its force at too high an elevation or too near the upper end of the wall.

It is noted that the apparatus is easily portable so as to conduct tests immediately at a job site within limited physical space. By doing this, there is no need to transport sample units from a plant or job site to a testing laboratory and wait a minimum of 24 hours for the samples to be tested, particularly since the test may or may not be relevant. Also, the apparatus could be set up at a block plant to sample units after their emergence from the curing system to determine the ability of the building units to withstand handling, for after all, the major resistance to yard chipping and cracking resides in the tensile strength of the building units. Additionally, the apparatus could be used to test sample units of varying ingredients to develop stronger units having lower cullage rates.

We claim:

1. The method of testing the tensile strength of the wall structure of a building block having a core opening comprising the steps of: placing a pair of opposed wallengaging members in engagement with opposite walls of said core opening, said members adapted to distribute applied force over a substantial portion of each engaged wall, providing force-applying means between said wall-engaging members, operating said forceapplying means to exert a force on said wall-engaging members only in a direction to move said pair of members away from each other and cause a tensile force to be applied to the non-engaged wall structures of the block until said non-engaged wall. structures fracture and measuring the force required to fracture said wall structure.

2. The method of claim 1 including the step of: locating said force-applying means along an axis substantially coincident with the center of gravity of said wall structure.

3. Apparatus for testing the tensile strength of the wall structure of a building unit having at least one core opening defined by opposed first walls connected by second walls, said apparatus comprising wall-engaging members engageable with said first walls on opposite sides of said core opening, force-applying means located between said members, means for distributing substantially uniform applied force: in a uniaxial direction over a major portion of said wall-engaging members and said first walls when force is applied to cause tensile forces to be applied to the second walls until the wall structure of the building unit fractures, and means associated with said force-applying means for measuring the force required to fracture said wall structure.

4. The structure of claim 3 in which said distributing means includes block means located between said wallengaging members and said force-applying means.

5. The structure of claim 4 in which each of said wallengaging members includes a pair of plate means adjustably connected together, said block means mounted on one of the plate means of each pair and overlying the other plate means, and said forceapplying means adapted to apply force against said block means.

6. The structure of claim 3 including means for supporting said force-applying means generally at the center of gravity of the wall structure.

7. The structure of claim 3 in which said forceapplying means includes a fluid operated ram having a piston and means for introducing fluid under pressure into said ram for extending said piston.

8. The structure of claim 3 including shim means selectively mounted within said core opening, whereby the effective operating range of said force-applying means is extended.

9. Apparatus for testing a continuous monolithic masonry frame having wall structure defining a core opening with opposed first walls connected by second walls, said apparatus comprising at least one wall-engaging member engaging a major portion of each of said first walls, ram means located between said wall-engaging members and adapted to apply an outward force in a uniaxial direction to said members, means intermediate said wall-engaging members and said ram means for distributing substantially uniform force to said members and said first walls, means for introducing fluid under pressure into said ram means until said wall structure fractures, and means for measuring the pressure required to fracture the wall structure, whereby an outward force from said ram means against said walls applies tensile forces only to said second walls. 

1. The method of testing the tensile strength of the wall structure of a building block having a core opening comprising the steps of: placing a pair of opposed wall-engaging members in engagement with opposite walls of said core opening, said members adapted to distribute applied force over a substantial portion of each engaged wall, providing force-applying means between said wall-engaging members, operating said force-applying means to exert a force on said wall-engaging members only in a direction to move said pair of members away from each other and cause a tensile force to be applied to the non-engaged wall structures of the block until said non-engaged wall structures fracture and measuring the force required to fracture said wall structure.
 2. The method of claim 1 including the step of: locating said force-applying means along an axis substantially coincident with the center of gravity of said wall structure.
 3. Apparatus for testing the tensile strength of the wall structure of a building unit having at least one core opening defined by opposed first walls connected by second walls, said apparatus comprising wall-engaging members engageable with said first walls on opposite sides of said core opening, force-applying means located between said members, means for distributing substantially uniform applied force in a uniaxial direction over a major portion of said wall-engaging members and said first walls when force is applied to cause tensile forces to be applied to the second walls until the wall structure of the building unit fractures, and means associated with said force-applying means for measuring the force required to fracture said wall structure.
 4. The structure of claim 3 in which said distributing means includes block means located between said wall-engaging members and said force-applying means.
 5. The structure of claim 4 in which each of said wall-engaging members includes a pair of plate means adjustably connected together, said block means mounted on one of the plate means of each pair and overlying the other plate means, and said force-applying means adapted to apply force against said block means.
 6. The structure of claim 3 including means for supporting said force-applying means generally at the center of gravity of the wall structure.
 7. The structure of claim 3 in which said force-applying means includes a fluid operated ram having a piston and means for introducing fluid under pressure into said ram for extending said piston.
 8. The structure of claim 3 including shim means selectively mounted within said core opening, whereby the effective operating range of said force-applying means is extended.
 9. Apparatus for testing a continuous monolithic masonry frame having wall structure defining a core opening with opposed first walls connected by second walls, said apparatus comprising at least one wall-engaging member engaging a major portion of each of said first walls, ram means located between said wall-engaging members and adapted to apply an outward force in a uniaxial direction to said members, means intermediate said wall-engaging members and said ram means for distributing substantially uniform force to said members and said first walls, means for introducing fluid under pressure into said ram means until said wall structure fractures, and means for measuring the pressure required to fracture the wall struCture, whereby an outward force from said ram means against said walls applies tensile forces only to said second walls. 